Keywords:
Infection, Diagnostic procedure, Nuclear medicine conventional, Musculoskeletal joint
Authors:
A. Arya, K. AGRAWAL; Watford/UK
DOI:
10.1594/essr2016/P-0093
Imaging findings OR Procedure Details
The most common cause of early failure (< 2years after initial surgery) are infection and instability.
More than 2 years after primary implantation,
the most common causes of failure are polyethylene wear and aseptic loosening.
Periprosthetic infection
The prevalence of deep infection after TKA is approximately 0.4-2% but it is higher (up to 10%) in revision arthroplasty.
The cause is usually haematogenous seeding associated with a distant infection.The diagnostic work-up for infection includes ESR and CRP and joint aspiration for suspected infection.
Radiographic findings of infection may vary from normal to bone destruction mimicking loosening.
Soft tissue gas,
secondary to gas-forming organisms is pathognomonic but rare.
Differentiating aseptic from infective loosening often cannot be made on plain radiographs.
Tc99m triple phase bone scan findings of infected TKR are increased uptake in all the three phases.
The lack of increased uptake on the first two phases mitigates against the diagnosis of infection.
Increased uptake on the first and second phases signifies hyperemia and increased blood pool uptake and are nonspecific.
In111 leukocyte scanning has a high sensitivity and negative predictive value approaching 95% and 100% respectively.
Indium labeled leukocytes accumulate in areas of inflammation or infection.
In addition,
the marrow surrounding the implanted joint prosthesis has been shown to have hyperplastic elements that often result in physiologic increased periprosthetic Indium uptake in the normal postoperative state.
It is therefore important to compare positive indium scans with a Tc-Sulphur Colloid marrow scan to improve accuracy andspecificity of the study.
If the indium and marrow scans match,
they are considered congruent and carry a low likelihood of infection.
If there is a mismatch,
where the areas of increased uptake on the indium scan are normal on the marrow scan,
the findings are considered incongruent and correlate with a high likelihood (>90%) of infection.
The treatment includes removal of the implant and cement and inseryionof an articulating cement antibiotic spacer along with 6 weeks of antibiotics followed by delayed reimplantation.
Aseptic loosening
It is the most common cause of delayed TKR failure.
Radiographic criteria include wide (greater than 2mm) or progressive periprosthetic radiolucency at the interface on follow-up radiographs. Tibial component loosening is more frequent than femoral component loosening.
Tc99m triple phase bone scan findings of aseptic loosening of TKR are increased uptake only in the third/delayed phase and not in the initial two phases.